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Light emitting device

a light-emitting device and light-emitting technology, applied in semiconductor devices, semiconductor/solid-state device details, instruments, etc., can solve the problems of inability to obtain a desired gray-scale, analog driving is extremely sensitive to fluctuation, and above-analog driving has a disadvantage of being extremely affected by tft characteristics fluctuation,

Inactive Publication Date: 2004-09-14
SEMICON ENERGY LAB CO LTD
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

This approach allows for consistent light emission across pixels, even with fluctuations in TFT characteristics, enabling clear multi-gray scale color display and reducing the degradation of EL layers, thus enhancing the performance of active matrix EL displays.

Problems solved by technology

However, the above analog driving has a disadvantage of being extremely affected by fluctuation in TFT characteristics.
As described above, the analog driving is extremely sensitive to fluctuation in characteristic of EL driver TFTs, which is a problem in the gray-scale display of a conventional active matrix EL device.
Therefore, even if the same gate voltage is applied, different currents (drain currents) are output, resulting in inconvenience that a desired gray-scale cannot be obtained.

Method used

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Examples

Experimental program
Comparison scheme
Effect test

embodiment 1

A case of performing 2.sup.6 gray scale display with a 6-bit digital video signal in an EL display according to the present invention is explained in Embodiment 1 using FIG. 5. Note that the EL display of Embodiment 1 has the structure shown in FIGS. 1 to 3.

First, the write in gate signal line Ga1 is selected in accordance with a write in gate signal input to the write in gate signal line Ga1 from the write in gate signal line driver circuit 103. The switching TFTs 107, all pixels (the first line of pixels) connected to the write in gate signal line Ga1 are then made an ON state.

At the same time, the first bit of a digital video signal is input to the source signal lines S1 to Sx from the source signal line driver circuit 102, and is input to the gate electrodes of the EL driver TFTs 108 through the switching TFTs 107.

When the digital video signal has "0" information, the EL driver TFTs 108 are made an OFF state in Embodiment 1. The power source electric potential is therefore not i...

embodiment 2

The order of appearance of the display periods Tr1 to Tr6 in a driving method of the present invention corresponding to a 6-bit digital video signal is explained in Embodiment 2.

FIG. 6 shows a timing chart of the driving method of Embodiment 2. Embodiment 1 may be referred to for detailed drive of the pixels, and therefore the explanation is omitted here. The longest non-display period (Td1 in Embodiment 2) within one frame period is provided at the end of the one frame period in the driving method of Embodiment 2. It appears to human eyes that there is a separation between the non-display period Td1 and the first display period (Tr4 in Embodiment 2) of the next frame period in accordance with the above structure. Unevenness of display, which occurs due to adjoining display periods for emitting light between adjacent frame periods, can thus be made more difficult for human eyes to recognize.

Note that, although a case for a 6-bit digital video signal is explained in Embodiment 2, the...

embodiment 3

A case of performing 2.sup.4 bit gray scale display with a 4-bit digital video signal in an EL display of the present invention is explained in Embodiment 3 using FIG. 7. Note that the EL display of Embodiment 3 has the structure shown in FIGS. 1 to 3.

First, the write in gate signal line Ga1 is selected in accordance with a write in gate signal input to the write in gate signal line Ga1 from the write in gate signal line driver circuit 103. The switching TFTs 107, all pixels (the first line of pixels) connected to the write in gate signal line Ga1 are then made an ON state.

At the same time, the first bit of a digital video signal is input to the source signal lines S1 to Sx from the source signal line driver circuit 102. The digital video signal is input to the gate electrodes of the EL driver TFTs 108 through the switching TFTs 107.

When the digital video signal has "0" information, the EL driver TFTs 108 are made an OFF state in Embodiment 3. The power source electric potential is ...

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Abstract

An active matrix light emitting device which is capable of clear color display of multiple gray scales is provided. The light emitting device has a pixel portion, and the pixel portion has a plurality of pixels. Each of the plurality of pixels has an EL element, a first EL driver TFT, a second EL driver TFT, a switching TFT, and an erasure TFT. The first EL driver TFT and the second EL driver TFT are connected in parallel.

Description

1. Field of the InventionThe present invention relates to an electronic display formed by fabricating an EL (electro luminescence) on a substrate, in particular, to an EL display using a semiconductor element (an element which uses a semiconductor thin film). Further, the present invention relates to a light emitting device using an EL display in a display portion.2. Description of the Related ArtRecently, a technique for forming TFTs on a substrate has been remarkably developed, and its application to an active matrix electronic display has been in proceeding. In particular, TFTs using a polysilicon film can operate at high speed, because such TFTs have a higher field effect mobility than TFTs using a conventional amorphous silicon film. Therefore, the control of pixels, which has been conventionally conducted by a driver circuit provided outside a substrate, can be performed by a driver circuit provided on the same substrate on which the pixels are provided.Such an active matrix e...

Claims

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Application Information

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Patent Type & Authority Patents(United States)
IPC IPC(8): G09G3/32G09G3/20
CPCG09G3/2022G09G3/3258G09G3/3275G09G3/3291H01L27/3262G09G3/2018G09G2300/0408G09G2300/0426G09G2300/0465G09G2300/0809G09G2300/0842G09G2300/0861G09G2310/0221G09G2310/0251G09G2310/027G09G2310/061G09G2320/0233G09G2320/043G09G2330/021H10K59/1213
Inventor INUKAI, KAZUTAKA
Owner SEMICON ENERGY LAB CO LTD
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